Astrocytic reaction to a lesion, under hormonal deprivation

Gonadal hormones can influence the morphology and function of glial cells, particularly astrocytes. Here we explore the hypothesis that 17beta-estradiol (E2) exerts a positive effect on astrocytes within the region of the cholinergic neurons of the basal forebrain, an area heavily implicated in memory and attentional processes. Female rats were ovariectomized at 3 months of age and lesioned with the immunotoxin 192 IgG-saporin before receiving a subcutaneous pellet containing 0.25mg of estrogen or placebo, released over 60 days. The control, non-ovariectomized group was treated identically. At the end of the treatment, we used image analysis procedures to evaluate changes in the levels of glial fibrillary acidic protein (GFAP) expression in the area of the lesion. Infusion of the immunotoxin induced a slight increase in GFAP expression in some subjects, compared to the contralateral side. However, when differences within animals where factored in, GFAP expression in ovariectomized animals treated with E2 was undistinguishable from intact controls. By contrast, in ovariectomized animals treated with placebo, GFAP expression was significantly higher. These results suggest that E2 deprivation may exacerbate the effects of an immunotoxic lesion, and, more importantly, that E2 administration may contribute to structural recovery of lesioned cholinergic neurons by blocking GFAP expression in the area. These results are particularly relevant in the context of female aging and postmenopausal dementia, and further highlight other potential levels at which to design interventions to preserve an intact cholinergic system, which may be crucial to prevent Alzheimer's disease.

Truncations of gelonin lead to a reduction in its cytotoxicity

Gelonin is a single chain ribosome-inactivating protein (RIP) with potential applications as a bullet of immunoconjugate for the treatment of cancer and AIDS. Using truncated forms of gelonin, we now report the relationship between its conformation and function. Circular dichroism (CD) and fluorescence spectra show that the N-terminus forms beta-sheets whereas the C-terminus contains alpha-helices of secondary structures. Biological experiments indicate that all gelonin truncation mutants lose partial toxicity compared to intact gelonin, an effect most strongly seen with C-terminally truncated gelonin. Similar evidence is also provided using a DNase-like activity assay. In addition, the intact gelonin exhibits the highest cytotoxicity to cancer cells. These results suggest that truncations of the terminal region of gelonin negatively regulate its function dominantly and that, due to its toxicity, intact gelonin is an important potential immunoconjugate.

The C-terminus of pokeweed antiviral protein has distinct roles in transport to the cytosol, ribosome depurination and cytotoxicity

Pokeweed antiviral protein (PAP) produced by pokeweed plants is a single-chain (type I) ribosome-inactivating protein (RIP) that depurinates ribosomes at the alpha-sarcin/ricin loop of the large rRNA, resulting in inhibition of translation. Unlike the type II RIPs, which have an active and a binding moiety, PAP has only the active moiety. The mechanism by which toxins without a binding moiety gain access to cytosolic ribosomes is not known. We set up yeast as a simple and genetically tractable system to investigate how PAP accesses ribosomes and showed that the mature form of PAP is targeted to the cytosol from the endomembrane system in yeast. In the present study, we performed a systematic deletion analysis to identify the signal required for transport of PAP to the cytosol. We demonstrate here that processing of the C-terminal extension and sequences at the C-terminus of the mature protein are critical for its accumulation in the cytosol. Using a series of PAP mutants, we identified the C-terminal signal and demonstrated that it is distinct from the sequences required for ribosome depurination and cytotoxicity. The C-terminal motif showed sequence similarity to type II RIPs that retrotranslocate from the endoplasmic reticulum to the cytosol. These results demonstrate that a conserved sequence at the C-terminus of a type I RIP mediates its transport to the cytosol and suggest that type I and II RIPs may use a common signal to enter the cytosol.

Multimodality molecular imaging of glioblastoma growth inhibition with vasculature-targeting fusion toxin VEGF121/rGel

Vascular endothelial growth factor A (VEGF-A) and its receptors, Flt-1/FLT-1 (VEGFR-1) and Flk-1/KDR (VEGFR-2), are key regulators of tumor angiogenesis and tumor growth. The purpose of this study was to determine the antiangiogenic and antitumor efficacies of a vasculature-targeting fusion toxin (VEGF(121)/rGel) composed of the VEGF-A isoform VEGF(121) linked with a G(4)S tether to recombinant plant toxin gelonin (rGel) in an orthotopic glioblastoma mouse model by use of noninvasive in vivo bioluminescence imaging (BLI), MRI, and PET.

METHODS

Tumor-bearing mice were randomized into 2 groups and balanced according to BLI and MRI signals. PET with (64)Cu-1,4,7,10-tetraazacyclododedane-N,N',N'',N'''-tetraacetic acid (DOTA)-VEGF(121)/rGel was performed before VEGF(121)/rGel treatment. (18)F-Fluorothymidine ((18)F-FLT) scans were obtained before and after treatment to evaluate VEGF(121)/rGel therapeutic efficacy. In vivo results were confirmed with ex vivo histologic and immunohistochemical analyses.

RESULTS

Logarithmic transformation of peak BLI tumor signal intensity revealed a strong correlation with MRI tumor volume (r = 0.89, n = 14). PET with (64)Cu-DOTA-VEGF(121)/rGel before treatment revealed a tumor accumulation (mean +/- SD) of 11.8 +/- 2.3 percentage injected dose per gram at 18 h after injection, and the receptor specificity of the tumor accumulation was confirmed by successful blocking of the uptake in the presence of an excess amount of VEGF(121). PET with (18)F-FLT revealed significant a decrease in tumor proliferation in VEGF(121)/rGel-treated mice compared with control mice. Histologic analysis revealed specific tumor neovasculature damage after treatment with 4 doses of VEGF(121)/rGel; this damage was accompanied by a significant decrease in peak BLI tumor signal intensity.

CONCLUSION

The results of this study suggest that future clinical multimodality imaging and therapy with VEGF(121)/rGel may provide an effective means to prospectively identify patients who will benefit from VEGF(121)/rGel therapy and then stratify, personalize, and monitor treatment to obtain optimal survival outcomes.

Decreased vesicular acetylcholine transporter and α4β2 nicotinic receptor density in the rat brain following 192 IgG-saporin immunolesioning

Degeneration of cholinergic neurons is a well known characteristic of Alzheimer's disease (AD). Two radioligands were studied in a rat model of cholinergic degeneration to evaluate their potential efficacy for molecular imaging of AD. Following specific cholinergic-cell immunolesioning with 192 IgG-saporin (SAP), ex vivo autoradiography was performed with (123)IBVM, a radioligand which targets the vesicular acetylcholine transporter (VAChT). Following the decay of (123)I, the same animals had in vitro autoradiography performed with (125)I-A-85380, a marker for nicotinic acetylcholine receptors (nAChRs). As expected significant, widespread decreases in (123)IBVM uptake were observed in SAP treated animals. Moderate but significant reductions in (125)I-A-85380 binding in the hippocampus (Hip) and cerebellum (Cbm) were also observed following SAP immunolesioning. The results with (123)IBVM confirm and extend previous work investigating the uptake of radioiodinated IBVM in this animal model. The results with (125)I-A-85380 are unique and are in contrast with work performed in this animal model with other nAChR radioligands, indicating the favourable properties of this radioligand for molecular imaging.

From anxiety to autism: spectrum of abnormal social behaviors modeled by progressive disruption of inhibitory neuronal function in the basolateral amygdala in Wistar rats

RATIONALE

Social behaviors are disrupted in several psychiatric disorders. The amygdala is a key brain region involved in social behaviors, and amygdala pathology has been implicated in disease states ranging from social anxiety disorder to autism.

OBJECTIVE

To test the effects of progressive disruption of the inhibitory function within the basolateral nucleus of the amygdala (BLA) on conspecific social interaction in rats and investigate functional networks from the ventral medial prefrontal cortex (mPFCv) to the BLA.

MATERIALS AND METHODS

BLA inhibitory tone was disrupted by priming it with the stress-peptide corticotrophin releasing factor (CRF) receptor agonist urocortin 1 (Ucn 1, 6 fmol), or by selective lesioning of a subset of BLA-GABAergic interneurons containing neurokinin 1 receptors using the targeted toxin SSP-Saporin. The effects of the disruption of GABAergic tone in the BLA were examined using a repeated exposure and habituation paradigm of social interaction (SI/h). Lesions and selectivity of lesions were confirmed postmortem. Additionally, effects of stimulating mPFCv on cFos activity in interneurons of the BLA were examined.

RESULTS

Rats primed with Ucn 1 showed persistent social inhibition, which could be overcome with habituation, putatively modeling social anxiety. Rats with a selective lesioning of a subset of GABAergic interneurons in the BLA exhibited persistent social inhibition that was not reversed by SI/h paradigm. We also demonstrate selective functional inputs to this subset of interneurons when mPFCv was activated.

CONCLUSIONS

These models with different gradations of disrupted BLA inhibition could help to study social dysfunction in disorders ranging from social anxiety to autism spectrum disorders.

Lesions to the nucleus basalis magnocellularis lower performance but do not block the retention of a previously acquired learning set

Rats were first trained to acquire an olfactory discrimination learning set (ODLS) on 40 olfactory-unique discrimination problems. Following acquisition of ODLS, animals were lesioned bilaterally in the nucleus basalis magnocellularis (nBM) using either quisqualic acid (QUIS) or 192 IgG-saporin (SAP). QUIS animals performed significantly worse than control animals following surgery and SAP animals performed transiently worse than control animals. Despite lowered performances, both QUIS and SAP animals performed significantly better than expected by chance on trial 2 indicating retention of the ODLS previously acquired. Implications for the role of the nBM in aspects of cognitive flexibility and its role in acquisition versus retention are discussed.

Guanidinylated neomycin delivers large, bioactive cargo into cells through a heparan sulfate-dependent pathway

Facilitating the uptake of molecules into living cells is of substantial interest for basic research and drug delivery applications. Arginine-rich peptides have been shown to facilitate uptake of high molecular mass cargos into cells, but the mechanism of uptake is complex and may involve multiple receptors. In this report, we show that a derivative of the aminoglycoside antibiotic neomycin, in which all of the ammonium groups have been converted into guanidinium groups, can carry large (>300 kDa) bioactive molecules across cell membranes. Delivery occurs at nanomolar transporter concentrations and under these conditions depends entirely on cell surface heparan sulfate proteoglycans. Conjugation of guanidinoneomycin to the plant toxin saporin, a ribosome-inactivating agent, results in proteoglycan-dependent cell toxicity. In contrast, an arginine-rich peptide shows both heparan sulfate-dependent and -independent cellular uptake. The high selectivity of guanidinoneomycin for heparan sulfate suggests the possibility of exploiting differences in proteoglycan compositions to target delivery to different cell types.

The rGel/BLyS fusion toxin specifically targets malignant B cells expressing the BLyS receptors BAFF-R, TACI, and BCMA

B lymphocyte stimulator (BLyS) is crucial for B-cell survival, and the biological effects of BLyS are mediated by three cell surface receptors designated B cell-activating factor receptor (BAFF-R), transmembrane activator and calcium modulator and cyclophilin ligand interactor (TACI), and B-cell maturation antibody (BCMA). Increased expression of BLyS and its receptors has been identified in numerous B-cell malignancies. We generated a fusion toxin designated rGel/BLyS for receptor-mediated delivery of the recombinant gelonin (rGel) toxin to neoplastic B cells, and we characterized its activity against various B-cell tumor lines. Three mantle cell lymphoma (MCL) cell lines (JeKo-1, Mino, and SP53) and two diffuse large B-cell lymphoma (DLBCL) cell lines (SUDHL-6 and OCI-Ly3) expressing all three distinct BLyS receptors were found to be the most sensitive to the fusion toxin (IC(50) = 2-5 pmol/L and 0.001-5 nmol/L for MCL and DLBCL, respectively). The rGel/BLyS fusion toxin showed specific binding to cells expressing BLyS receptors and rapid internalization of the rGel component into target cells. The cytotoxic effects of rGel/BLyS were inhibited by pretreatment with free BLyS or with soluble BAFF-R, TACI, and BCMA decoy receptors. This suggests that the cytotoxic effects of the fusion toxin are mediated through BLyS receptors. The rGel/BLyS fusion toxin inhibited MCL cell growth through induction of apoptosis associated with caspase-3 activation and poly (ADP-ribose) polymerase cleavage. Our results suggest that BLyS has the potential to serve as an excellent targeting ligand for the specific delivery of cytotoxic molecules to neoplastic B cells expressing the BLyS receptors, and that the rGel/BLyS fusion toxin may be an excellent candidate for the treatment of B-cell malignancies especially MCL and DLBCL.

Solution behavior of a novel biopharmaceutical drug candidate: a gonadotropin-toxin conjugate

There is little known about the solution structure and stability of peptide-protein conjugates, which comprise a new class of potential biopharmaceutical agents. This study describes the solution behavior of gonadotropins-releasing hormone (GnRH) chemically conjugated to pokeweed antiviral protein (PAP). The conjugate adopts a well-defined conformation across a pH range of 4 to 8. Even after heating to 80 degrees C, the conjugate retains a significant amount of secondary and tertiary structure. Heating for 1 h at 60 degrees C does lead to chemical damage, as determined by cation exchange chromatography. Using an experimental design approach, the optimal pH and salt concentration for limiting chemical damage was determined.

Long-term effects of neonatal basal forebrain cholinergic lesions on radial maze learning and impulsivity in rats

We examined long-term behavioural effects of neonatal lesions of the cholinergic basal forebrain obtained by intracerebroventricular injections of 192 IgG saporin (192 IgG-Sap). Five-month-old Wistar male rats (injected with 192 IgG-Sap or phosphate-buffered saline on postnatal day 7) were tested using operant chambers with two nose-poking holes, delivering one food pellet immediately or five pellets after a delay. The length of delay progressively increased over days (from 0 to 100 s). When compared with controls, 192 IgG-Sap rats showed a slight preference for smaller immediate over larger delayed rewards, thus indicating elevated intolerance to delay (i.e. more impulsivity). Sibling animals were tested in a computerized radial maze (baited vs. nonbaited arm procedure). 192 IgG-Sap rats appeared slower than controls in accomplishing the task. The neonatal 192 IgG-Sap lesion did not alter cortical levels of serotonin and/or its metabolites, but induced a marked cortical cholinergic loss. Our data suggest that a prolonged basal forebrain cholinergic hypofunction produces (i) an impairment in cognitive performances that is detectable only when highly complex tasks are used; (ii) a slight enhancement of the impulsive behavioural profile. This animal model may thus be useful to investigate some cognitive deficits and other secondary symptoms seen in Alzheimer's disease.

Distinct mechanisms mediating methamphetamine-induced neuronal apoptosis and dopamine terminal damage share the neuropeptide substance p in the striatum of mice

Methamphetamine (METH) is an addictive psychostimulant that induces damage to the dopamine terminals and the apoptosis of some neurons of the striatum. Our laboratory demonstrated using either a single bolus dose (30 mg/kg) or a binge (10 mg/kg 4x at 2-h intervals) of METH that pharmacological blockade of the substance P receptor (neurokinin-1) attenuates METH-induced damage to both the presynaptic dopamine terminals and the apoptosis of some neurons of the striatum. To determine the phenotype of striatal neuron ablated by METH, we combined TUNEL (Terminal Deoxyncleotidyl Transferase-Mediated dUTP Nick End Labeling) with immunofluorescence for selective markers of projection and interneurons. METH induces the loss of approximately 20% of the projection neurons. The cholinergic and gamma-aminobutyric acid (GABA)-parvalbumin interneurons sustain losses of 30% and 50%, respectively. The somatostatin/neuropeptide Y (NPY)/nitric oxide synthase (NOS) interneurons are not impacted by METH. To investigate the mechanism by which substance P mediates METH-induced damage in this part of the brain, we ablated the striatal interneurons that express the neurokinin-1 receptor (NK-1R) with the selective neurotoxin substance P-SAP. Ablation of the NK-1R-expressing interneurons prevented METH-induced apoptosis in the striatum but was without effect on depletion of dopamine terminal markers. We propose that substance P mediates the apoptosis of some striatal neurons via the intrastriatal activation of nitric oxide synthesis. In contrast, substance P may mediate damage of the dopamine terminals via an extrastriatal mechanism involving the substantia nigra and cortical glutamate release.

Selective depletion of cortical noradrenaline by anti-dopamine beta-hydroxylase-saporin impairs attentional function and enhances the effects of guanfacine in the rat

RATIONALE

Previous data indicate that depletion of cortical noradrenaline (NA) impairs performance of an attentional five-choice serial reaction time task (5CSRT) under certain conditions. This study employed a novel immunotoxin, anti-dopamine-beta hydroylase (DbetaH)-saporin, to make relatively selective lesions of the noradrenergic projections to the prefrontal cortex (PFC) in rats trained to perform the 5CSRT.

OBJECTIVES

The aim of this work is to examine (1) the effect of cortical noradrenaline depletion on sustained attentional performance in the 5CSRT under a variety of test conditions and (2) the effects of guanfacine, a selective alpha-2 adrenoceptor agonist on attentional performance in sham and NA-depleted rats.

MATERIALS AND METHODS

Animals received either intramedial prefrontal anti-DbetaH-saporin or vehicle and were tested on the baseline task with a variety of additional manipulations including (1) decreasing target duration, (2) increasing rate and (3) temporal unpredictability of target presentation and (4) systemic guanfacine.

RESULTS

Anti-DbetaH-saporin infused into the PFC produced a substantial loss of DbetaH-positive fibers in that region and in other adjacent cortical areas. There was no significant depletion of DA or 5-HT. NA-depleted animals were not impaired on the baseline task, but were slower to respond correctly under high event rate conditions, and their discriminative accuracy was reduced when stimulus predictability decreased. Guanfacine significantly reduced discriminative accuracy in NA-depleted animals only.

CONCLUSION

Selective cortical NA depletion produced deficits on the 5CSRT test of sustained attention, especially when the attentional load was increased and in response to systemic guanfacine. These results are consistent with a role of coeruleo-cortical NA in the regulation of effortful attentional processes.

Selective cholinergic depletion of the hippocampus spares both behaviorally induced Arc transcription and spatial learning and memory

We demonstrated previously that when hippocampal-dependent learning and plasticity are compromised by fornix lesions, behaviorally induced expression of the immediate early gene, Arc, is correspondingly low. The medial septum and the vertical diagonal band are major sources of subcortical afferents that innervate the hippocampus via the fornix. Here we assessed the specific contribution of cholinergic afferents from these regions to the impairments in spatial learning and behavioral induction of Arc transcription produced by fornix lesions. The immunotoxin, 192 IgG-saporin, was used to produce selective lesions of cholinergic cell bodies in the medial septum and vertical diagonal band. Rats were then trained on both cued and spatial delayed match-to-place tasks in a radial arm water maze. Animals with 192 IgG-saporin lesions learned both cue and place discrimination tasks in the water maze normally, and showed only a mild and transient impairment when switching from the cued to the spatial version of the task. Following behavioral testing, rats explored two novel environments sequentially in a setting known to induce Arc expression in hippocampal pyramidal neurons. In marked contrast to the effects of complete fornix transection, quantitative in situ autoradiography revealed no differences in Arc mRNA expression between sham and lesion animals in CA1, CA3 or stratum radiatum. The conclusion from these data is that cholinergic deafferentation alone cannot account for the spatial learning deficits or impaired behavioral induction of Arc transcription produced by fornix lesions.

Cholinergic modulation of sensory interference in rat primary somatosensory cortical neurons

Sensory interaction was studied using extracellular recordings from 275 neurons in the primary somatosensory (SI) cortex of pentobarbital-anesthetized rats. Tactile stimulation was applied to the receptive field using a 1 mm diameter probe that indented the skin for 20 ms, at 0.5 Hz, (test stimulus). Tactile test responses of SI neurons decreased during simultaneous application of a gentle tickling (distracter stimuli) continuously for 60 s on a separate receptive field located in the same or the contralateral hindlimb (ipsi- or contralateral distraction). This decrease in neural response produced by distracter stimuli was interpreted as "sensory interference". Sensory interference was observed in 66% and 61% of recorded SI neurons when ipsi- or contralateral distracters were applied, respectively and was blocked by a novel stimulus obtained by increasing the stimulation frequency of the test tactile stimuli from 0.5 to 2 Hz. The number of neurons showing sensory interference in response to a contralateral distracter was not modified after corpus callosum transection, suggesting that interhemispheric connections are not crucial for sensory interference. In contrast, the number of neurons showing sensory interference decreased in animals with 192 IgG-saporin basal forebrain lesions that decreased the number of cortical cholinergic fibers. This finding indicates that cholinergic afferents from the basal forebrain are fundamental to sensory interference and suggests that the associative cortices - basal forebrain - sensory cortices network may be implicated in sensory interference.

Effect of selective cholinergic denervation on the serotonergic system: implications for learning and memory

The cholinergic system has been widely implicated in cognitive processes and cholinergic loss is a classical hallmark in Alzheimer disease. Increasing evidence supports a role of the serotonergic system in cognition, possibly through a modulation of cholinergic activity. We compared selective cholinergic denervation by administration of the immunotoxin 192 IgG-saporin in the nucleus basalis of Meynert (NBM) with intracerebroventricular (ICV) lesions of the basal forebrain in male rats 7 days after lesioning. NBM lesions induced significant changes in cholinergic markers in the frontal cortex, whereas ICV lesions produced significant decreases in cholinergic markers both in the frontal cortex and hippocampus. Only ICV lesions lead to memory impairments in passive avoidance and Morris water maze tasks. Both models lead to reductions of serotonin levels in the frontal cortex. Similar changes in 5-hydroxytriptophan levels were observed, suggesting a downregulation of the rate-limiting enzyme for the synthesis of serotonin along with the cholinergic deficit. Neither 5-HT1A nor 5-HT1B receptors seem to mediate this process. These data imply that the serotonergic system in the frontal cortex can compensate for diminished cholinergic function and support the investigation of the serotonergic system as a therapeutic target to treat Alzheimer disease.

Effects of hypocretin-1 in 192-IgG-saporin-lesioned rats

Hypocretin, also known as orexin, is a neuropeptide located in the perifornical region of the lateral hypothalamus; this region projects to all the major arousal centres including the basal forebrain. The basal forebrain contains a mixed population of neurons, some of which are cholinergic. To identify the relative contribution of the noncholinergic neurons to arousal, here we utilized 192-IgG-saporin to lesion the basal forebrain cholinergic neurons and determine whether microinjection of hypocretin-1 to the basal forebrain is still effective in inducing arousal. In Sprague-Dawley rats given 192-IgG-saporin (intraventricular, 6 microg; n=7) 92% of the basal forebrain cholinergic neurons were destroyed compared to nonlesioned rats (n=5). In the lesioned rats microinjection of hypocretin-1 (0.0625, 0.125 or 0.25 nmol in 250 nL) to the basal forebrain increased waking and suppressed sleep (both non-REM and REM) in a concentration-dependent manner and to the same extent as in nonlesioned rats. These results suggest that, in the absence of the basal forebrain cholinergic neurons, the basal forebrain noncholinergic neurons are able to convey hypocretin's arousal signal unabated.

Substance P-saporin down-regulates substance P receptor immunoreactive sensory dorsal root ganglion neurons innervating the lumbar intervertebral discs in rats

STUDY DESIGN

To examine changes in substance P receptors on dorsal root ganglion cells innervating the rat lumbar intervertebral discs using immunohistochemistry and a retrograde neurotracing method.

OBJECTIVE

We evaluated the effects of intradiscal administration of substance P-saporin, a toxin selective for cells expressing substance P receptors.

SUMMARY OF BACKGROUND DATA

The rat L5/6 intervertebral disc is multi-segmentally innervated from the L1-L6 dorsal root ganglions. Substance P and the neurokinin-1 receptor contribute to inflammatory pain transmission. Substance P immunoreactive-sensory nerve fibers in human intervertebral discs and immunoreactive-dorsal root ganglion neurons innervating rat intervertebral discs have been reported to be important in the transmission of discogenic low back pain. In the current study, we evaluated the effects of intradiscal administration of substance P-saporin, a toxin selective for cells expressing substance P receptor.

METHODS

Sixteen rats were used (control group, n = 8; substance P-saporin group, n = 8). To detect dorsal root ganglion neurons innervating the L5/6 intervertebral disc, neurotracer (fluoro-gold crystals) was placed into the intervertebral disc. Seven days after fluoro-gold application, the L5/6 intervertebral disc was exposed and injected with 175 ng of sterile substance P-saporin (substance P-saporin group, n = 8). Fourteen days after the first operation, each dorsal root ganglion was harvested, sectioned, and processed for neurokinin-1 immunohistochemistry using rabbit antibody to neurokinin-1. The numbers of fluoro-gold labeled neurons, and fluoro-gold labeled and neurokinin-1 immunoreactive neurons were counted in both groups.

RESULTS

Neurons innervating the L5/6 intervertebral discs, retrogradely labeled with fluoro-gold, were distributed throughout dorsal root ganglions from L1 to L6 in both groups. Of fluoro-gold labeled neurons, the proportion of neurokinin-1 immunoreactive neurons was 35% in the control group. However, the proportion of neurokinin-1 immunoreactive neurons was 8% after administration of substance P-saporin into the intervertebral discs (substance P-saporin group). Substance P-saporin significantly decreased the ratio of neurokinin-1 immunoreactive neurons.

CONCLUSION

Substance P-saporin decreased the ratio of neurokinin-1 immunoreactive neurons innervating the disc related to discogenic low back pain. Substance P-saporin may be a useful tool to investigate the mechanism of discogenic low back pain.

Overexpression of biologically active VEGF121 fusion proteins in Escherichia coli

Vascular endothelial growth factor-A (VEGF) exists as five different isoforms, which exert their growth stimulatory effects through interaction with the FLK and KDR receptors. The VEGF(121) isoform has been employed as a highly selective carrier of therapeutic agents to target tumor endothelial cells resulting in inhibition of tumor growth and metastasis. VEGF(121) and VEGF(121)/rGel fusion toxin containing hexa-histidine tags were expressed in Escherichia coli AD494 (DE3) pLysS. Media containing glycerol as a primary carbon source increased the specific expression levels of soluble VEGF(121) and VEGF(121)/rGel (mg/L/OD10) by more than two-fold over LB media when grown in a batchtype cultivation in a bioreactor. High cell densities over OD 40 were achieved using a fed-batch method and employing feeding medium containing glycerol and yeast extract. The overall production of the target proteins was improved 18-fold for VEGF(121) (59.2mg/L) and 27-fold for VEGF(121)/rGel (42.5mg/L), respectively, compared to the conventional flask cultivation method (3.3 and 1.6mg/L for VEGF(121) and VEGF(121)/rGel, respectively). The purified VEGF(121) and VEGF(121)/rGel fusion proteins were biologically active as assessed by phosphorylation of KDR receptors and cytotoxicity against KDR expressing cells.

The differential catalytic activity of ribosome-inactivating proteins saporin 5 and 6 is due to a single substitution at position 162

Saporin, a type I ribosome-inactivating protein produced by the soapwort plant Saponaria officinalis belongs to a multigene family that encodes its several isoforms. The saporin seed isoform 6 has significantly higher N-glycosidase and cytotoxic activities compared with the seed isoform 5, although the two have identical active sites. In the present study, we have investigated the contribution of non-conservative amino acid changes outside the active sites of these isoforms towards their differential catalytic activity. The saporin 6 residues Lys134, Leu147, Phe149, Asn162, Thr188 and Asp196 were replaced by the corresponding saporin 5 residues, Gln134, Ser147, Ser149, Asp162, Ile188 and Asn196, to generate six variants of saporin 6, K134Q, L147S, F149S, N162D, T188I and D196N. By functional characterization, we show that the change in amino acid Asn162 in saporin 6 to aspartic acid residue of saporin 5 contributes mainly to the lower catalytic activity of saporin 5 compared with saporin 6. The non-involvement of other non-conservative amino acids in the differential catalytic activity of these isoforms was confirmed with the help of the double mutations N162D/K134Q, N162D/L147S, N162D/F149S, N162D/T188I and N162D/D196N.

Up-regulation of cation-independent mannose 6-phosphate receptor and endosomal-lysosomal markers in surviving neurons after 192-IgG-saporin administrations into the adult rat brain

The cation-independent mannose 6-phosphate receptor (CI-MPR) is a single transmembrane domain glycoprotein that plays a major role in the trafficking of lysosomal enzymes from the trans-Golgi network to the endosomal-lysosomal (EL) system. Because dysfunction of EL system is associated with a variety of neurodegenerative disorders, it is possible that the CI-MPR may have a role in regulating neuronal viability after toxicity/injury. In the present study, we report that 192-IgG-saporin-induced loss of basal forebrain cholinergic neurons causes a transient up-regulation of CI-MPR protein levels in surviving neurons of the basal forebrain and frontal cortex but not in the brainstem region, which was relatively spared by the immunotoxin. This was accompanied by a parallel time-dependent increase in other EL markers, ie, cathepsin D, Rab5, and LAMP2 in the basal forebrain region, whereas in the frontal cortex the levels of cathepsin D, and to some extent Rab5, were increased. Given the critical role of the EL system in the clearance of abnormal proteins in response to changing conditions, it is likely that the observed increase in the CI-MPR and components of the EL system in surviving neurons after 192-IgG-saporin treatment represents an adaptive mechanism to restore the metabolic/structural abnormalities induced by the loss of cholin-ergic neurons.

Spinal NK-1 receptor expressing neurons mediate opioid-induced hyperalgesia and antinociceptive tolerance via activation of descending pathways

Opioids can induce hyperalgesia in humans and in animals. Mechanisms of opiate-induced hyperalgesia and possibly of spinal antinociceptive tolerance may be linked to pronociceptive adaptations occurring at multiple levels of the nervous system including activation of descending facilitatory influences from the brainstem, spinal neuroplasticity, and changes in primary afferent fibers. Here, the role of NK-1 receptor expressing cells in the spinal dorsal horn in morphine-induced hyperalgesia and spinal antinociceptive tolerance was assessed by ablating these cells with intrathecal injection of SP-saporin (SP-SAP). Ablation of NK-1 receptor expressing cells prevented (a) morphine-induced thermal and mechanical hypersensitivity, (b) increased touch-evoked spinal FOS expression, (c) upregulation of spinal dynorphin content and (d) the rightward displacement of the spinal morphine antinociceptive dose-response curve (i.e., tolerance). Morphine-induced hyperalgesia and antinociceptive tolerance were also blocked by spinal administration of ondansetron, a serotonergic receptor antagonist. Thus, NK-1 receptor expressing neurons play a critical role in sustained morphine-induced neuroplastic changes which underlie spinal excitability reflected as thermal and tactile hypersensitivity to peripheral stimuli, and to reduced antinociceptive actions of spinal morphine (i.e., antinociceptive tolerance). Ablation of these cells likely eliminates the ascending limb of a spinal-bulbospinal loop that engages descending facilitation and elicits subsequent spinal neuroplasticity. The data may provide a basis for understanding mechanisms of prolonged pain which can occur in the absence of tissue injury.

The growth factor fusion construct containing B-lymphocyte stimulator (BLyS) and the toxin rGel induces apoptosis specifically in BAFF-R-positive CLL cells

The cytokine B lymphocyte stimulator (BLyS) mediates its effect through cell-surface receptors BAFF-R, TACI, and BCMA. BLyS receptors are expressed only on B cells and not present in other normal cells including normal T lymphocytes. Chronic lymphocytic leukemia (CLL) is a B-cell disease and CLL lymphocytes express BLyS receptors. Gelonin, a type 1 ribosome-inactivating toxin, lacks cell membrane binding domain and hence is nontoxic to intact cells. We generated a construct of recombinant gelonin (rGel) fused to BLyS to specifically target quiescent B-CLL lymphocytes. The construct rGel/BLyS specifically binds and internalizes through BAFF-R into CD19(+) B-CLL lymphocytes and induces apoptosis at nanomolar concentrations. In contrast, rGel alone was not able to internalize into these leukemic lymphocytes. Mechanistically, the rGel/BLyS construct inhibits protein synthesis with an IC(50) of less than 3 nM compared with more than 5000 nM for rGel toxin alone. This rGel/BLyS-mediated decrease in protein synthesis was associated with a decline in short-lived proteins such as MCL-1 and XIAP, the 2 survival proteins in B-CLL. There was a strong relationship between a decrease in these proteins and the cleavage of PARP, a hallmark feature of apoptosis. Taken together, these data suggest that the rGel/BLyS fusion toxin may have potential therapeutic efficacy for B-CLL patients.

Inhibition of Prostate Tumor Growth and Bone Remodeling by the Vascular Targeting Agent VEGF121/rGel

The pathophysiology of tumor growth following skeletal metastases and the poor response of this type of lesion to therapeutic intervention remains incompletely understood. Vascular endothelial growth factor (VEGF)-A and its receptors play a role in both osteoclastogenesis and tumor growth. Systemic (i.v.) treatment of nude mice bearing intrafemoral prostate (PC-3) tumors with the vascular ablative agent VEGF(121)/recombinant gelonin (rGel) strongly inhibited tumor growth. Fifty percent of treated animals had complete regression of bone tumors with no development of lytic bone lesions. Immunohistochemical analysis showed that VEGF(121)/rGel treatment suppressed tumor-mediated osteoclastogenesis in vivo. In vitro treatment of murine osteoclast precursors, both cell line (RAW264.7) and bone marrow-derived monocytes (BMM), revealed that VEGF(121)/rGel was selectively cytotoxic to osteoclast precursor cells rather than mature osteoclasts. VEGF(121)/rGel cytotoxicity was mediated by Flt-1, which was down-regulated during osteoclast differentiation. Analysis by flow cytometry and reverse transcription-PCR showed that both BMM and RAW264.7 cells display high levels of Flt-1 but low levels of Flk-1. Internalization of VEGF(121)/rGel into osteoclast precursor cells was suppressed by pretreatment with an Flt-1 neutralizing antibody or by placenta growth factor but not with an Flk-1 neutralizing antibody. Thus, VEGF(121)/rGel inhibits osteoclast maturation in vivo and it seems that this process is important in the resulting suppression of skeletal osteolytic lesions. This is a novel and unique mechanism of action for this class of agents and suggests a potentially new approach for treatment or prevention of tumor growth in bone.

Lack of localization of 5-HT6 receptors on cholinergic neurons: implication of multiple neurotransmitter systems in 5-HT6 receptor-mediated acetylcholine release

The involvement of the cholinergic system in learning and memory together with the cognitive enhancing properties of 5-HT6 receptor antagonists led us to study the relationship between 5-HT6 receptors and cholinergic neurotransmission. A selective cholinergic lesion, induced by injection of the immunotoxin 192-IgG-Saporin into the nucleus basalis magnocellularis, failed to alter the density of 5-HT6 receptor mRNA or protein expression in the deafferentated frontal cortex, suggesting that 5-HT6 receptors are not located on cholinergic neurons. The 5-HT6 receptor antagonist SB-357134 (0.001-1 microM) induced a concentration-dependant K+-evoked [3H]acetylcholine (ACh) release in vitro in rat cortical and striatal slices, which was blocked by tetrodotoxin. SB-357134, up to 1 microM, stimulated glutamate release in cortical and striatal slices. In the cortex, riluzole (1 microM) blocked the SB-357134-induced K+-stimulated [3H]ACh release, and simultaneous administration of MK-801 (1 microM) and SB-357134 (0.05 microM) elicited an increase in K+-evoked ACh release. In the striatum, SB-357134, 1 microM, decreased dopamine release, and the increase in K+-evoked [3H]ACh release induced by 5-HT6 receptor blockade was reversed by the D1 receptor antagonist, SCH23390 (1 microM). In both the frontal cortex and striatum, bicuculline, 1 microM, showed no effect on SB-357134-evoked [3H]ACh. These results are discussed in terms of neurochemical mechanisms involved in 5-HT6 receptor functions.